Selection of proper mounting media for examining heterogeneous copolymers with the phase microscope

A technique for examining heterogeneous copolymers with the phase microscope is described. This method is based on the use of a mounting medium that displays selective solubility toward the constituent materials, thereby masking one or more phases in order to provide suitable phase contrast and isolation of the constituent to be examined.     

The effects of anti-rheumatoid drugs on the in vitro activity of human serum hyaluronidase

Fourteen antirheumatoid drugs were tested for their effects on the in vitro hyaluronidase activity of normal human serum. Four drugs produced significant changes in enzyme activity. Different results were obtained with ovine testicular hyaluronidase when diluted with either saline or inactivated human serum. No increase in serum hyaluronidase activity was found in patients with rheumatoid arthritis. There was no evidence for the existence of tissue specific isoenzymes of hyaluronidase in the serum of either normal subjects or patients with rheumatoid arthritis.     

Thermodynamic Constants for Association of Isomeric Chlorobenzoic and Toluic Acids With 1,3-Diphenyl-guanidine in Benzene

This paper reports values of ΔF₂₅, ΔH, and ΔS₂₅ for the association of diphenylguanidine with the isomeric monochlorobenzoic acids and the isomeric toluic acids in benzene from spectrophotometric measurements at 25 and 30 °C, using bromophthalein magenta E (3′, 5′, 3″, 5″-tetrabromophenolphthalein ethyl ester) as the indicator. The results are compared with available data for other donor-acceptor associations in aprotic solvents which include the monomer-dimer equilibrium of benzoic acids, the association of tertiary amines with iodine, and the association of certain oxygen bases with phenols. The comparisons indicate that the value of the ratio ΔH/298ΔS is approximately constant in the following associations in aprotic solvents: (1) Association of phenolic or carboxylic acids with nitrogenous bases to form hydrogen bonded ion-pairs; (2) hydrogen bonding of weakly acidic phenols to nitrogenous bases; (3) association of tertiary amines with iodine. A somewhat smaller value for this ratio seems to apply to most associations of phenols with oxygen bases. Possible applications of these findings include estimation of other thermodynamic constants when one of the constants ΔF, ΔH, or ΔS is known, and clarification of the relative importance of ionic and covalent contributions in hydrogen bond formation.     

Biochemical and Structural Characterization of XoxG and XoxJ and Their Roles in Lanthanide-Dependent Methanol Dehydrogenase Activity

Lanthanide (Ln)-dependent methanol dehydrogenases (MDHs) have recently been shown to be widespread in methylotrophic bacteria. Along with the core MDH protein, XoxF, these systems contain two other proteins, XoxG (a c-type cytochrome) and XoxJ (a periplasmic binding protein of unknown function), about which little is known. In this work, we have biochemically and structurally characterized these proteins from the methyltroph Methylobacterium extorquens AM1. In contrast to results obtained in an artificial assay system, assays of XoxFs metallated with La^III, Ce^III, and Nd^III using their physiological electron acceptor, XoxG, display Ln-independent activities, but the K_m for XoxG markedly increases from La to Nd. This result suggests that XoxG′s redox properties are tuned specifically for lighter Lns in XoxF, an interpretation supported by the unusually low reduction potential of XoxG (+172 mV). The X-ray crystal structure of XoxG provides a structural basis for this reduction potential and insight into the XoxG–XoxF interaction. Finally, the X-ray crystal structure of XoxJ reveals a large hydrophobic cleft and suggests a role in the activation of XoxF. These studies enrich our understanding of the underlying chemical principles that enable the activity of XoxF with multiple lanthanides in vitro and in vivo.